Pancreatic cancer is a major public health problem with approximately 57,600 new cases in 2020. Five-year survival is less than 9% for all stages, with surgical resection the only potentially curative therapy. Nonetheless, a clear majority of patients are not candidates for surgery due to locally advanced disease or metastatic spread, and ultimately derive little to no survival benefit from radiation or chemotherapy.
Advances in cancer immunotherapy have revolutionized cancer care, providing hope in the form of durable cancer regression and long-term survival. In patients with treatment refractory metastatic melanoma, immunotherapy in the form of adoptive transfer with tumor infiltrating immune cells (TIL therapy) has yielded practice changing response rates, with complete remission in 10-20% of patients.
Unfortunately, an immune response to pancreatic cancer has been elusive in most clinical trials, and thus identifying methods to enhance the immune response to cancer has been the focus of our research program in the last two decades. Recent transient responses to TIL therapy in pancreatic cancer obtained at the NCI Surgery Branch and our institution have revitalized our interest in improving TIL therapy outcomes.
A tumor’s ability to evade the immune system can be attributed to an immunosuppressive tumor microenvironment and downregulation or loss of the major histocompatibility complex (MHC), which is required by immune cells to recognize malignant cells. Conventional immunotherapy approaches, including TIL therapy, rely on activation and tumor specific recognition of T cells with alpha-beta T cell receptors that require intact MHC expression. However, with 60% of primary and 90% of metastatic pancreatic tumors exhibiting mutated or reduced expression of MHC molecules, new immunotherapy approaches are necessary to elicit improved treatment responses. Gamma Delta (gd) T cells are an understudied tissue resident immune subset that can recognize a broad range of antigens without the presence of MHC molecules.
Gamma Delta T cells comprise as much as 40% of tumor infiltrating lymphocytes in pancreatic cancer and display potent antitumor immunity. Utilizing the resources of our world-renowned pancreatic cancer treatment center and established cell therapy production facility, we aim to evaluate the efficacy of gd TIL therapy for patients with metastatic pancreatic cancer. After developing a clinical grade cell manufacturing protocol to grow gd TIL and compare tumor specific reactivity with alpha beta TIL, we aim to conduct a pilot Phase I/II clinical trial assessing the safety and preliminary treatment efficacy of gd TIL therapy. We will also identify MHC independent TCRs from gd TIL for further development as universal gene therapies.
Ultimately, this study will define the therapeutic potential of tumor infiltrating gd T cells, helping to advance pancreatic cancer into a disease that our own immune system, ‘the best doctor’ can control.
Major types of immunotherapy include checkpoint blockade, adoptive cell transfer, recombinant cytokines, and cancer vaccines. However, only a fraction of patients show sustained clinical responses.
These challenges demand new types of immunotherapies that are more potent and specific. Very recently, we have developed CRISPRa-mediated Multiplexed Activation of Endogenous Genes as an Immunotherapy (MAEGI) (Wang*, Chow* et al. 2019 Nature Immunology).
Neoantigen-targeting approaches demonstrated leveraging personalized neoantigens based on delivery of synthetic mutant peptides or transcripts. However, the efficacy and scalability of these approaches is limited. The CRISPR activation (CRISPRa) system uses a catalytically inactive Cas9 (dCas9), enabling simple and flexible gene expression regulation through dCas9-transcriptional activators paired with single guide RNAs (sgRNAs). This enables precise targeting of large gene pools of endogenous genes in a flexible manner. We demonstrate that MAEGI has therapeutic efficacy across three tumor types.
Pancreatic cancer is a challenging cancer type currently with few options. Based on the broad mechanism of action, we reason that MAEGI may apply to pancreatic cancer. We propose to develop MAEGI specifically for pancreatic cancer immune gene therapy at pre-clinical stage.
First, we will be generating lineage-specific expression vectors and CRISPRa libraries for targeting pancreatic cancer cells with MAEGI. Then, we will be testing PDAC-p-MAEGI’s in vivo efficacy in syngeneic pancreatic cancer models. Finally, we will be studying MAEGI’s mechanism of action in the tumor microenvironment in syngeneic pancreatic cancer models.
To our knowledge MAEGI is an entirely novel form of cancer immune gene therapy. Therefore, this is a high-risk, high-reward project. This project if successful may bring innovative treatment options, albeit at early stage, for pancreatic cancer and other forms of tough cancer types.
This Alliance for Cancer Gene Therapy Research Fellow is funded in part by Swim Across America.
Few procedures are available for physicians to rapidly and reliably harness immune responses to fight cancer. For example, bioinformatics tools can predict cancer proteins that T cells could react with, but vaccines developed from them commonly fail because the immunized patients do not have enough T cells that are inherently able to recognize the predicted antigens.
The goal of our research is to develop injectable nanoreagents that can genetically program T cell receptors (TCRs) into circulating lymphocytes, enabling them to recognize cancer proteins. Specifically, we hypothesize that customized cancer-targeting can be introduced into immune cells by combining anti-cancer vaccines with techniques that induce endogenous CD8 T cells to express TCRs specific for the vaccines, and consequently provide them with the ability to react with cancer cells. We further hypothesize that this platform can be used to program helper cells with defined “MHC class-II-restricted TCRs”, and thereby improve responses to tumor antigens compared to conventional immunization methods.
Our multidisciplinary team of immunologists, bioengineers and geneticists has already established that injected nanoparticles can deliver engineered TCR genes into host T cells in a way that, once they are stimulated by vaccines, the lymphocytes recognize cancer antigens. Following rapid vaccine-induced expansion, these programmed cells continue to differentiate into long-lived memory T lymphocytes.
We propose to develop a suite of nanoparticle reagents that can rapidly establish anti-cancer immunity by programming in situ specific receptors into the patient’s T cell pool. To achieve this, we will pursue the following Specific Aims:
(1) to improve our efficiency for introducing vaccine specificity into circulating CD8+ T cells; (2) to establish that this approach boosts immune responses; and (3) to determine if our methods promote the regression of cancer regardless of the patient’s pre-existing TCR landscape.
To assure the medical relevance of our findings, we will (i) program the lymphocytes to express an affinity-optimized receptor specific for the tumor antigen mesothelin, and (ii) use them to treat a genetically engineered mouse model that faithfully recapitulates human pancreatic ductal adenocarcinoma from inception to invasion.
We believe that the data, reagents, and application methods generated by our research will provide the basis for a broad repertoire of gene modification systems that can generate selective immunity against cancer and other diseases.
Our group is exploring the use of gene therapy techniques to engineer viruses to stimulate the immune system to fight pancreatic cancer. In this proposal we will modify a vaccinia virus (similar to the virus used to immunize against smallpox) to produce hormones that attract a certain kind of tumor fighting immune cell called T cells to the sites of tumor.
We have already administered a similar virus to patients and found that it is able to be delivered through the blood stream safely, travel to sites of tumor and infect the tumor cells. We have also shown that a special way to stimulate the immune system to generate tumor fighting T cells called aDC1 is effective in patients with a very aggressive kind of brain tumor.
In this study we will combine these two approaches (stimulate T cells with aDC1 and attract them to the tumor with the vaccinia virus) in patient who have pancreatic cancer. There are several clinical trials examining immunotherapy for pancreatic cancer in progress at this time, we believe our approach will be a significant improvement on current trials.